To simplify manufacturing and reduce overall costs, an electronic system is generally manufactured on separate printed circuit boards. These separate printed circuit boards are then connected to one another by electrical connectors. Typically, one printed circuit board serves as a backplane. Then other printed circuit boards, which are often called daughter boards or daughter cards, are connected to the backplane by electrical connectors to form the electronic system.
To meet demands for electronic systems that are more compact, faster, and more complex, progressively more circuits are placed within a given area of each printed circuit board, and those additional circuits operate at increasingly higher frequencies. Therefore, the electrical connectors between the printed circuit boards have to pass data at increasingly higher rates and higher signal frequencies. For faster data processing, current electronic systems require faster data transmission between printed circuit boards.
Because of the increasing signal frequencies, electrical connectors encounter more electrical noise. The electrical noise often manifests itself as signal reflections, crosstalk, electromagnetic radiation, or other similar forms of electrical noise. Signal reflection occurs when a portion of a signal being transmitted is reflected back to the signal source instead of being transmitted to the signal destination. Signal reflections are caused by signal path imperfections that give rise to impedance mismatching. Also, changes in the signal path characteristics, particularly abrupt changes, can cause signals to be reflected.
Crosstalk is electromagnetic coupling of one signal path with another signal path. The coupling results in one signal affecting another nearby signal. To reduce electrical noise in the form of crosstalk, signal paths are arranged so that the signal paths are spaced farther apart from each other and nearer to a shield plate which is generally the ground plate or a conductor connected to ground, such as described in U.S. Patent Application Pub. No. 2004/0264153 to Payne et al., entitled “Printed Circuit Board for High Speed, High Density Electrical Connector with Improved Cross-Talk Minimization, Attenuation and Impedance Mismatch Characteristics,” which is incorporated by reference herein in its entirety. Therefore, the signal paths tend to couple electromagnetically more with the shield plate or ground conductor and less with each other. For a particular level of crosstalk, the signal paths can be placed closer to each other as long as sufficient electromagnetic coupling to the shield plate or a ground conductor is maintained.
Also, in a region where the signal path electrically connects to another circuit, manufacturing costs are relatively higher since the signal path must be formed and shaped to provide an acceptable electrical connection that is mechanically durable. Such connections are typically more difficult to manufacture because a more complicated shape is required and complicated shapes are more costly to form. The connections also need electromagnetic coupling to the shield plate or to ground conductors to minimize crosstalk.
An electrical connector is described in U.S. Pat. No. 6,409,543 to Astbury, Jr. et al., entitled “Connector Molding Method and Shielded Waferized Connector Made Therefrom,” the entire disclosure of which is incorporated herein by reference. The electrical connector is assembled from wafers, and each wafer is formed by molding a dielectric housing over a shield plate. Signal conductors are inserted into the dielectric housing. A mating contact region is provided near an edge of the wafer where the signal conductors mate with a backplane connector. In the mating contact region, the signal conductors mate with the signal contacts of the backplane connector. Provided near the edge of the wafer are shield beam contacts. The shield beam contacts are connected to the shield plate and engage an upper edge of the shield plate in the backplane connector that forms a current path to reduce crosstalk. However, the shield beam contact provides only a single current path to reduce electromagnetic coupling and crosstalk, and a substantial amount of the shield plate is not utilized, thereby diminishing the effectiveness of the shield plate.
Another approach to provide shielding between adjacent connections and to reduce costs is to use plastic containing conductive materials, such as the connector described in U.S. Patent Application Pub. No. 2007/0042639 to Manter et al. entitled “Connector with Improved Shielding in Mating Contact Region,” which is incorporated by reference herein in its entirety. However, the use of plastic containing conductive materials between signal paths does not provide the stiffness, the shielding, and the lower relative manufacturing cost of using a metal shield.
Therefore, there is a need in the art for a high speed, high density electrical connector design that minimizes crosstalk, provides increased conductive metal content around the contact region, and lowers manufacturing costs.